The ability to manufacture semiconductor devices in great quantity and at small scale has revolutionized the electronics industry. There is a continual need to maximize the quality and lifetime of semiconductor devices. During the operation of a semiconductor device, a major cause of performance degradation is the “hot electron effect”, also referred to as “hot carrier effects”, in which high-energy electrons (or holes) cause defects in the semiconductor device. A variety of explanations have been advanced to describe the mechanism of this phenomenon, including the generation of traps, and the creation of dangling-bonds. For example, in transistor semiconductor devices, the performance degradation likely caused by the hot electron effect can include a slow change in the threshold voltage, a decrease in transconductance, and leakage.
Hydrogen may be found in semiconductor devices as a result of exposure to hydrogen during and after the manufacturing process. This exposure allows hydrogen to fill defects in the lattice-structure of the semiconductor device, and the general process is referred to as passivation, with hydrogen being the passivating species in this particular example. Passivation replaces dangling-bonds in the semiconductor device with chemical bonds between the semiconductor device and the passivating species. Passivation of a semiconductor device can improve its performance, including by making behavior characteristics of the device more consistent, by increasing the lifetime of the device, and by making operating characteristics of the device more desirable. Passivation of a semiconductor device generally occurs during the manufacturing process of the device, but passivation can occur at any time.
The hot electron effect may be mitigated by passivating a semiconductor device with a passivating species other than hydrogen. For example, it is known that the use of deuterium as a passivating species diminishes the hot electron effect. Lynding et al. noted that replacing hydrogen with deuterium during the final wafer sintering process reduces hot electron degradation effects in metal oxide semiconductor transistors. (See, “Reduction of Hot Electron Degradation in Metal Oxide Semiconductor Transistors by Deuterium Processing” Applied Physics Letters, Vol. 68, No. 18, Apr. 29, 1996, pp. 2526-2528.) Hess et al. correlated reduced hot electron degradation with the use of deuterium instead of hydrogen for passivation. (See, “Giant Isotope Effect in Hot Electron Degradation of Metal Oxide Silicon Devices” IEEE Transactions on Electron Devices, Vol. 45, No. 2, February 1998, pp. 406-416, and “Reductions of Hot Electron Degradation in Metal Oxide Semiconductor Transistors by Deuterium Processing” Applied Physics Letters, Vol. 68, No. 18, April 1996, 2526-2528.)
While deuterium passivation moderates the hot electron effect, deuterium can only chemically bond at the appropriate sites of the semiconductor device if those sites are available for chemical bonding. The ubiquity of hydrogen in gases that have not been mostly or completely purified, and also in ambient air, means that unless significant effort is used in isolating the semiconductor device from hydrogen, at least partial if not complete hydrogen passivation of dangling-bonds will occur, thus at least partially if not completely preventing deuterium passivation of the device. In order to allow for partial or complete replacement of one passivating species with another, at least some of the chemical bonds between the semiconductor device and the undesired passivating species must be broken. Therefore, current techniques for deuterium passivation generally include subjecting the device to heat, often near about 350-600 degrees C., in order to thermally cleave chemical bonds between the semiconductor device and hydrogen, creating dangling-bonds which could then be passivated by deuterium, (see, e.g. U.S. Pat. No. 6,017,806 (Harvey)). This heat treatment is often performed in the presence of deuterium in the form of a gaseous deuterium source or in the form of a film or a layer, in a solid or liquid or vapor state, which contains a deuterium source, such that deuterium may diffuse to the appropriate chemical bonding sites in the semiconductor device, and such that hydrogen may diffuse away from those sites, (see, e.g., U.S. Pat. No. 5,972,765 (Clark et al.)). In the use of these techniques, the quantity of chemical bonding sites that become occupied by deuterium is generally proportional to the amount of time that the semiconductor device is subjected to the heat treatment. These techniques are problematic because, among other issues, high temperatures can create thermal defects in the devices, thereby potentially reducing yield of the manufacturing process or decreasing quality. Also, high temperature treatment is non-selective, in that the entire device may be heated, imparting thermal energy to the entire device. As a result, thermal energy is imparted to other chemical bonds in the semiconductor device, possibly thermally cleaving these chemical bonds as well, including chemical bonds between the semiconductor device and deuterium or another desired passivating species.
Another less common method for cleaving chemical bonds between a semiconductor device and an undesired chemical species prior to passivation with a desired chemical species involves the use of an electrical prestress, as described by Cheng et al. in Applied Physics Letters, Vol. 77, No. 15, October 2000, 2358-2360. The prestress technique subjects a semiconductor device to electrical stress of a strength and duration sufficient to allow the hot electron effect to cleave a desired amount of chemical bonds between the semiconductor device and hydrogen. The prestress technique is time-consuming, and also generally requires probing of the semiconductor device to permit subjection of the device to the electrical stress, which can be both inconvenient and also impractical, e.g., especially for large numbers of densely distributed semiconductor devices, as found in most integrated circuits.
U.S. Patent Publication No. 2009/0069611 (Lukehart) describes a method of forming reactive sites on an adsorbate-substrate by non-thermal, non-electronic resonant photodesorption of a gas from the adsorbate-substrate; reacting the reactive sites with a functional radical; and cyclically repeating the steps of forming and reacting. The method is not disclosed or suggested to be used to passivate a semiconductor device following photodesorption of a gas. Additionally, the method is not disclosed or suggested to be used to passivate any material with deuterium after photodesorption of a gas.
Infrared light tuned to a particular frequency is known to selectively cleave chemical bonds between silicon and hydrogen. (See, e.g., Liu et al., Science, May 2006, 312, 1024-1026). This reference does not, however, disclose or suggest that after the method of chemical bond-cleavage between silicon and hydrogen, subsequent passivation with another chemical species may be performed.